Fittings are used for connecting thermally insulated pipes, as they are e.g. used for transporting cooled media like water. These fittings consist of an inner part through which the medium flows, mostly a hollow body made of polyethylene (PE). This hollow body is surrounded on the outside entirely by a thermally insulating material, mostly polyurethane (PU), except for its openings for the medium. These fittings are consequently thermally insulated in order to avoid that environment air heats up the cooled medium. No condensed water shall be able to form on the surface of the fitting and the surface must additionally be mechanically robust in order to withstand the stress during mounting, for the reason which often a shell made of PE is used, which is located on the thermal insulation. The fittings may have different shapes. Accordingly, straight connections exist, but also curved shapes or T-pieces are needed. In many cases, these fittings have additional channels leading to the outside, which have to remain open on the top side. These channels serve as contacts for cables connected during mounting and in this way enable an electrical welding of the fitting ends to the pipe ends.
Manufacture of such composite parts can be carried out by introducing the inner part into the PE-shell and by surrounding it with foam with a suitable material after having centered it in the middle. Thereby it is problematic that curved or branched inner parts cannot be processed in this way, because positioning inside the prefabricated PE-shell cannot be achieved. Hence, this method is only universally usable for straight pieces not having contacts for electrical welding. A further disadvantage is the necessity to have to provide the PE-shell. These parts have to be injection-moulded in a complex way. Furthermore, the wall thickness of the PE-shell is relatively large, resulting in a high material cost.
DE 10153855 A1 describes a method by means of which a moulded body is backfilled only partially at a defined location, after the surface of the mould was provided with a decorative coating at this location, which later forms the surface of the finished part. This function of this surface in primarily decorative, a special mechanical robustness is not mentioned. The used foam has no thermally insulating function.
Instead of a finish, which is sprayed into the mould, a mould skin may also be introduced, which then forms the surface of the finished composite part. This is e.g. described in DE 102007061643 A1. The necessity of having to manufacture the mould skin in a separate work step is a disadvantage of this method. Besides, a one-component PU-system is used, which has to be tempered in order to harden.
EP 1190828 A1 describes a similar method but with the difference that the mould is constructed of multiple parts, thus simplifying the removal of more complex composite parts with undercuts.
U.S. Pat. No. 5,223,193 A claims a method in case of which a reactive isocyanate/polyol-mixture is applied on the mould. Subsequently, the mould rotates in order to achieve a uniform distribution on the surface and thereafter the foaming is performed with a second PU-system. In this method, no inner part is surrounded by foam.
U.S. Pat. No. 5,580,501 A describes how a first layer of PU-based powder finish is applied in a mould. This method also requires tempering in order to melt the powder finish and to make it react. Inner parts surrounded with foam are not provided.
US 2005244628 A describes how a soft object can be manufactured by also first applying a coating in a mould and subsequently applying a second coating with a different polymer. Hard foam is not used here.